Conventional paint rollers are composed of two parts: a wire roller that freely spins on an axle as the roller moves across a surface, and a roller cover, which is a fabric-covered cylinder that slips onto the wire roller. The wire roller has a handle for the user to grasp. When attached to the wire roller, the roller cover is made to absorb the paint/coating from a reservoir, such as a paint pan. This absorbed coating is then applied to a surface by a rolling action. Currently, application of liquid surface coatings such as paint use a fabric covered roller to rapidly apply these coatings to surfaces. While these rollers work well on flat surfaces, they cannot be used to apply surface coatings in corners where two walls meet, where walls meet ceiling or where walls meet trim.
To overcome this limitation of conventional rollers a number of corner painting devices have been patented. These corner-painting rollers are of three basic types:                1. rollers which have the paint fabric solidly attached to the roller,        2. rollers wherein the fabric is not solidly attached to the roller, and        3. rollers that use adhesives to attach the fabric.        
For rollers with fabric solidly attached, the roller is assembled with nuts and bolts, requiring tools for assembly, which may not be readily available. Additionally, the nuts and bolts tend to get covered with coating material and can fail to work properly. Disassembly can be difficult and messy, and the protruding nuts and bolts can damage the surface being coated.
With the corner painting roller where the fabric is not solidly attached to the roller cover, the fabric fits over the body of the roller, which is then attached to the roller axle. This is a two-step assembly process. When this roller is in use, the fabric is not anchored in place and can warp or become completely detached from the cover body marring the wall finish and resulting in messy cleanups.
The corner roller employing adhesives requires a multi-step assembly to apply dual fabric surfaces and application of the adhesive to the roller body. This reduces the flexibility of textures once the fabric is permanently affixed. In addition, this corner roller requires an adaptor to fit into a conventional paint pan.
All of the above are limited in that the coating would be transferred to both joined surfaces. In the case of painting the joint between wall and ceiling or wall and trim, the undesirable result would be coating transferred where not desired. These corner rollers are also limited to 90° or greater joints.
In addressing trim applications, two basic types have been patented:                1. a wheeled edge flat sponge pad or bristle surface, and        2. a roller with a paddle mounted so that it swivels into place on the edge of the roller, supposedly to protect the trim from being coated.        
The flat pad trim applicator works well in protecting the trim from being coated, but the texture and finish do not match that of the roller normally being used on the rest of the surface.
The roller with the swivel barrier invariably becomes coated on the trim side with excess coating and transfers the coating to the surface not desired to be coated.